Degradation of human calcitonin in human plasmas.

The degradation in vitro of human calcitonin (HCT) in plasma from normal subjects and patients with disorders of calcium metabolism was studied. As measured by radioimmunoassay, the hormone was stable at 37°C in phosphate buffer for 24 hr but progressively disappeared when incubated in normal human plasma. The loss was temperature and pH dependent, being maximal at 37°C between pH 6.0 and 7.0. Under these conditions ¹²⁵I-HCT appeared to be degraded to at least one labeled fragment that behaved on polyacrylamide gels as if it were smaller than 1000 daltons. The rate of formation of this fragment correlated well with the rate of loss of immunoreactive HCT. Compared to plasma from normal individuals, plasma from patients with hypercalcemia due to causes other than hyperparathyroidism degraded HCT significantly more rapidly. The mean loss of HCT in 5 hr in plasma from nine such patients was 54% ± 17% (± 2 SEM), compared to 22% ± 5% in plasma from 22 healthy volunteers (p < 0.001). Those patients whose plasma most rapidly degraded HCT had milkalkali syndrome, metastatic carcinoma of the colon, metastatic oat cell carcinoma of the lung, and metastatic breast carcinoma. Rates of HCT degradation in plasma from eight hypercalcemic patients with hyperparathyroidism and seventeen normocalcemic patients with malignancy were within the normal range. From these findings we conclude that human plasma contains one or more enzymes that degrade HCT and that the hormone is degraded more rapidly in plasma from some patients with hypercalcemia.     

Immunochemical heterogeneity of calcitonin in plasma.

Calcitonin was measured in the plasma of 13 patients with medullary throid carcinoma and one patient with a calcitonin-producing islet cell carcinoma of the pancreas. The hormone was measured by the simultaneous application of two calcitonin antisera which had differing specificity. Calcitonin measurements were also made of gel filtration (Bio Gel P30) fractions of plasma samples. Although the two antisera were of comparable sensitivity for the measurement of human calcitonin standards, they reacted differently with the calcitonin in the plasma samples. One antiserum (LD-1) gave consistently higher estimations of hormone concentration in the plasma of patients with medullary thyroid carcinoma than the other (LD-26). By contrast, the concentration of calcitonin from the islet cell carcinoma of the pancreas was higher in the LD-26 assay. Multiple gel filtration peaks of immunoreactive calcitonin activity were present in both thyroidal and nonthyroidal calcitonin. Furthermore, the two different antisera identified differing immunochemical peaks of calcitonin activity for agiven plasma sample. These findings demonstrate the presence of immunochemical heterogeneity in plasma calcitonin and suggest the presence of immunological differences between thyroidal and nonthyroidal calcitonin.     

Concentration of plasma calcium in response to human calcitonin in female rats during aging.

The effects of aging and estradiol on the concentration of plasma calcium in response to human calcitonin (hCT) were investigated in rats. Old (20 months) and young (2 months) female rats were catheterized via the right jugular vein and the left femoral vein before an infusion of 1 nM hCT (0.1 ml/min) into the left femoral vein. Young ovariectomized (Ovx) rats were injected subcutaneously with estradiol benzoate (EB, 25 micrograms/kg) or oil once daily for 3 days before hCT challenge. Blood samples were collected from the jugular catheter before and after the hCT infusion. The basal level of plasma calcium was not affected by age. The infusion of 1 nM hCT decreased the plasma calcium concentration by 18% in old and by 29% in young female rats. The post-infusion levels of plasma calcium were comparatively higher in old rats than in young rats (p less than .05 at 30 min and p less than .02 at 90 min). In young rats, the responses of plasma calcium to hCT infusion were reduced after ovariectomy. Short-term estrogen injection, however, did not restore the sensitivity of young Ovx rats to the CT infusion. These findings suggest that the plasma calcium level in response to calcitonin is decreased in rats during aging. The reduction of the hypocalcemic effect of calcitonin in old female rats at least was estradiol-independent.     

Basal plasma immunoreactive calcitonin in postmenopausal osteoporosis

Calcitonin (CT) deficiency has been suggested as an etiologic factor in postmenopausal osteoporosis (PM-OP). Basal immunoreactive calcitonin (iCT) was measured with a sensitive radioimmunoassay (RIA) in 62 PM-OP women with compressin fractures (CF) and in 28 normal age-matched women. Mean iCT values in the two groups were not significantly different (43.5 and 45.1 pg/ml, p > 0.10). In the 62 PM-OP females, no significant correlation was noted between basal plasma iCT levels and (1) age; (2) severity of disease as assessed by number of CF; (3) serum calcium, phosphorus, alkaline phosphatase, and immunoreactive parathyroid hormone; and (4) total bone mass as assessed by neutron activation analysis determinations of total body calcium (TBC). In 20 PM-OP patients treated for 24 mo with 100 Medical Research Council (MRC) units daily of synthetic salmon CT, no correlation was observed between basal plasma iCT and response of bone mass (TBC) to therapy. These data suggest that basal CT is not decreased in women with PM-OP, and that the level of circulating CT does not influence therapeutic changes in bone mass during CT therapy. CT is probably not a major etiologic or pathogenetic factor in PM-OP.     

Immunoextracted calcitonin in milk and plasma from totally thyroidectomized women. Evidence of monomeric calcitonin in plasma during pregnancy and lactation

The level of immunoreactive calcitonin in the first produced breast milk was in totally thyroidectomized (TX) women 713 +/- 307 pg-eq/ml (mean +/- SD, N = 7) and in control women 772 +/- 329 pg-eq/ml (N = 33), i.e. about 45 times higher than in plasma (see below). On gel chromatography of immunoextracted milk from TX women, immunoreactive calcitonin appeared as high molecular weight forms in the same pattern as in milk from healthy women when the same antiserum was used for immunoextraction and radioimmunoassay (RIA). In another series of experiments, a new antiserum raised in rabbits was used for measurement of immunoreactive calcitonin after immunoextraction with 1. Plasma levels of immunoreactive calcitonin in the TX women during pregnancy were 16 +/- 6 pg-eq/ml (N = 6) and during lactation 14 +/- 7 pg-eq/ml (N = 5). Immunoreactive calcitonin was undetectable (less than 8 pg/ml) in plasma from those TX women in whom lactation had stopped (N = 5). Immunoextraction and gel chromatography of plasma collected during pregnancy and lactation from the TX women showed that the immunoreactive calcitonin present eluted in the region of monomeric calcitonin with both antiserum 1 and 2. In conclusion, high concentrations of high molecular weight forms of of immunoreactive calcitonin have been demonstrated in milk from TX patients, most probably devoid of any calcitonin-producing thyroid C-cells. This points to a local production site in the mammary gland.(ABSTRACT TRUNCATED AT 250 WORDS)     

Re-examination of human calcitonin radioimmunoassay

Evaluations of human immunoreactive calcitonin (IRCT) assay have been extensively reviewed. Labelled hormone was re-purified on carboxymethyl-cellulose in order to isolate a fraction containing mainly monoiodinated calcitonin, which was found to be very stable. Two antisera with different immunochemical characteristics were used for incubation studies, one of which was incubated with unextracted and extracted plasma samples. The sensitivity of the assays was 60 pg/ml plasma. However, marked differences were observed in the results obtained by the three methods depending on the importance of the inhibitory effect of plasma on the binding of the tracer to antibodies. However, the absolute plasma IRCT level could not be related to the presence of calcitonin M, except in one case. Further studies are needed in order to ascertain the origin and the significance of the immunoreactive material which was detected in normal plasma by one antiserum.     

Identification of calcitonin receptors in human spermatozoa

Calcitonin (CT) is a powerful hypocalcemic hormone which regulates calcium balance in cells. The presence of CT and CT receptors has been demonstrated in many extrathyroidal tissues, including the male genital tract. CT immunoreactivity has also been found in human seminal fluid, and an inhibitory effect of salmon CT on human sperm motility in vitro was recently reported. In this study the presence of specific binding sites for synthetic salmon CT in intact human spermatozoa was investigated using [125I]salmon CT. Binding experiments demonstrated a CT-sperm interaction involving a receptor-mediated mechanism. The binding was very rapid and minimally reversible, with the maximal site saturation occurring at approximately 2 nM labeled peptide. The dissociation of the CT-receptor complex was only slightly influenced by the addition of unlabeled hormone. Increasing concentrations of unlabeled salmon, eel, and human CT produced a dose-dependent inhibition of [125I]salmon CT binding. These data fulfill the major criteria for demonstration of specific receptors for salmon CT in human spermatozoa. Owing to the key role of calcium ions in regulating sperm motility and the onset of the acrosomal reaction, CT receptors could be important in male gamete physiology.     

Heterogeneity of immunoreactive calcitonin in human milk

Immunoreactive calcitonin (ICT) has been detected in human milk by radioimmunoassay (RIA), using antibodies raised against synthetic human calcitonin (hCT). The level of ICT was 10-40 times higher than the reference level of human serum. Gel chromatography of human milk disclosed a molecular weight heterogeneity of ICT, with at least two forms larger than the monomer (Mr greater than 70000 and 30000 approximately). The 30000 peak constituted the major fraction of ICT. No detectable amount of ICT was coeluted with [125I]CT. Reduction with disulphide cleaving agents, denaturation or acidification did not alter the gel chromatographic properties of ICT, while tryptic digestion caused partial degradation of ICT and formation of new ICT molecules with an approximate molecular weight of 6000.     

Response of Paget's disease to human calcitonin in patients resistant to porcine calcitonin

Eleven patients with Paget's disease of bone, treated intermittently for 2-4 years with porcine calcitonin (pCT) and clinically resistant to pCT [no modifications of serum alkaline phosphatase (ALP) and urinary hydroxyproline ( uHOP ) during pCT administration] were treated with 0.5-0.25 mg/day of human calcitonin (hCT) for 3-6 months. Nine of our patients showed biochemical improvement during the first 2 months of treatment, with reduction in ALP and uHOP . In one patient with slightly increased ALP and uHOP , and in another one during the second treatment course, hCT treatment did not modify the biochemical indices of bone disease. However all patients, including those with biochemical resistance, experienced a remarkable diminution of bone pain, which had not been observed during previous pCT treatment courses. Therefore, hCT appears to be indicated for therapeutic use in patients who are resistant to foreign calcitonins.     

Intracerebroventricular administration of human calcitonin and human calcitonin gene-related peptide inhibits meal-stimulated gastric acid secretion in the dog

This study was designed to assess the central nervous system actions of human calcitonin (hCalc) and human calcitonin gene-related peptide (hCGRP) on meal-stimulated gastric acid secretion in awake beagle dogs. hCalc (0.1–1.0 nmol/kg) and hCGRP (0.01–1.0 nmol/kg) injected into the third cerebral ventricle significantly inhibited gastric acid secretion stimulated by an 8% peptone meal. hCGRP was ten times more potent than hCalc in inhibiting gastric secretion. Neither hCalc nor hCGRP significantly altered plasma gastrin concentrations compared to control values. Truncal vagotomy did not prevent the gastric inhibitory actions of hCalc and hCGRP. Ganglionic blockade with chlorisondamine completely abolished the gastric inhibitory action of hCalc but had no effect on gastric acid inhibition induced by hCGRP. The results of this study indicate that intracerebroventricular administration of hCalc and hCGRP inhibits meal-stimulated gastric acid secretion in awake dogs. Inhibition of gastric acid secretion by hCalc and hCGRP in the dog is not mediated by inhibition of gastrin release or by the vagus nerves. Human Calc but not human CGRP appears to inhibit meal-stimulated gastric acid secretion in the dog by activation of the autonomic (sympathetic) nervous system.     

Efficacy of intranasal human calcitonin in patients with Paget's disease refractory to salmon calcitonin

PURPOSE: A cause for the resistance to intranasal salmon calcitonin (sCT) therapy in patients with Paget's disease is the occurrence of neutralizing antibodies to sCT. As a result, a new formulation of intranasal human calcitonin (hCT) was developed, and the efficacy investigated in patients treated earlier with sCT. PATIENTS AND METHODS: Twelve patients with Paget's disease were treated twice daily for 6 months with 1 mg synthetic hCT administered intranasally. Five patients demonstrated low-titer antibodies to sCT, and four of the patients did not respond previously to 1-year therapy with intranasal sCT. The hypocalcemic effect of 3 mg hCT was compared to that of 0.1 mg sCT before and after the intranasal hCT therapy. Serum alkaline phosphatase and the ratio between the urinary excretion of hydroxyproline and creatinine were measured before and during intranasal hCT treatment. RESULTS: The hypocalcemic response to 3 mg intranasal hCT (-6.60 +/- 0.67%, mean +/- standard error) was similar before and at the end of intranasal hCT therapy (-5.92 +/- 0.80%, p greater than 0.1). Intranasal sCT (0.1 mg) lowered serum calcium less effectively (-2.86 +/- 0.76%) than 3 mg intranasal hCT (p less than 0.05). The presence of low-titer antibodies to sCT did not affect the hypocalcemic response to sCT or hCT. As a result of the 6-month intranasal hCT regimen, serum alkaline phosphatase and urinary hydroxyproline/creatinine ratio were reduced to 62 +/- 5% (p less than 0.001) and 80 +/- 7% (p less than 0.05) respectively, of pretreatment levels. In four patients previously resistant to intranasal sCT therapy because of neutralizing antibodies to sCT, serum alkaline phosphatase was similarly lowered by intranasal hCT to 66 +/- 6% of pretreatment levels (p less than 0.05). CONCLUSION: A new formulation of intranasal hCT effectively lowered serum calcium levels, alkaline phosphatase concentrations, and urinary hydroxyproline excretion in patients with Paget's disease, some of whom were previously resistant to intranasal sCT because of neutralizing antibodies.     

Detection of mRNA encoding calcitonin, calcitonin gene related peptide and proopiomelanocortin in human tumors

Expression of the calcitonin (CT)/calcitonin gene related peptide (CGRP) gene and the proopiomelanocortin (POMC) gene has been demonstrated by Northern blot hybridization analysis of RNA extracted from human medullary thyroid carcinoma (MTC), pheochromocytoma and lung carcinoma. CT mRNA in these tumors could not be distinguished in size from CT mRNA isolated from normal human thyroid tissue. CGRP mRNA (previously demonstrated in 12 out of 12 lung tumor cell lines investigated) could not be detected in 13 primary lung tumors or 10 metastases thereof. The length of POMC mRNA in MTCs (present in all 4 metastases investigated but not in 7 primary tumors) and pheochromocytomas is about 100 nucleotides more than pituitary POMC RNA. In lung tumors 2 POMC RNA species can be detected, one of the same size as in pituitary tissue and one about 100 nucleotides larger.